An upper limit on the frequency of short-period black hole companions to Sun-like stars

Creators: Green, Matthew J.¹; Ziv, Yoav²; Rix, Hans-Walter¹; Maoz, Dan²; Hamoudy, Ikram³; Mazeh, Tsevi²; Faigler, Simchon²; Lam, Marco C.⁴; El-Badry, Kareem⁵; Hume, George^{6, 7}; Munday, James⁸; Yarker, Paige^{6, 7}

1. Max Planck Institute for Astronomy
2. Tel Aviv University
3. Bar-Ilan University
4. University of Edinburgh
5. California Institute of Technology
6. Isaac Newton Group
7. University of Sheffield
8. University of Warwick

Abstract

Stellar-mass black holes descend from high-mass stars, most of which had stellar binary companions. However, the number of those binary systems that survive the binary evolution and black hole formation is uncertain by multiple orders of magnitude. The survival rate is particularly uncertain for massive stars with low-mass companions, which are thought to be the progenitors of most black hole X-ray binaries. We present a search for close black hole companions (orbital period ≲3 days, equivalent to separation ≲20 R_⊙) to AFGK-type stars in TESS; that is, the non-accreting counterparts to and progenitors of low-mass X-ray binaries. Such black holes can be detected by the tidally induced ellipsoidal deformation of the visible star, and the ensuing photometric light curve variations. From an initial sample of 4.7 × 10⁶TESS stars, we have selected 457 candidate ellipsoidal variables with large mass ratios. However, after spectroscopic follow-up of 250 of them, none so far are consistent with a close black hole companion. On the basis of this non-detection, we determine (with 2σ confidence) that fewer than one in 10⁵ solar-type stars in the solar neighbourhood hosts a short-period black hole companion. This upper limit is in tension with a number of ‘optimistic’ population models in the literature that predict short-period black hole companions around one in ∼10^4 − 5 stars. Our limit is still consistent with other models that predict only a few in ∼10^7 − 8.

Copyright and License

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Open Access funding provided by Max Planck Society.

Acknowledgement

We thank the anonymous reviewer for their feedback which has improved the quality of the manuscript. We also thank Dominick Rowan for comments on a pre-print of this work. We are grateful to the European Southern Observatory and Isaac Newton Group of Telescopes staff for the additional support provided for operations during the COVID-19 pandemic. MJG and HWR acknowledge support from the European Research Council through ERC Advanced Grant No. 101054731. MJG and DM acknowledge further funding under the European Union’s FP7 Programme, ERC Advanced Grant No. 833031. This work is based in part on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 108.226R. The NTT is operated by ESO at Cerro La Silla. INT observations were obtained under proposal I/2022A/13. The INT is operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA’s Science Mission Directorate. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This work has made use of the software TOPCAT and the PYTHON packages NUMPY, MATPLOTLIB, SCIPY, ASTROPY, EMCEE (Foreman-Mackey et al. 2013), ASPIRED (Lam et al. 2023), SPARTA (Shahaf et al. 2020), and PHOEBE (Prsa & Zwitter 2005).

Data Availability

Full Tables 3 and 4 are are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/695/A210.

Software References

This work has made use of the software TOPCAT and the PYTHON packages NUMPY, MATPLOTLIB, SCIPY, ASTROPY, EMCEE (Foreman-Mackey et al. 2013), ASPIRED (Lam et al. 2023), SPARTA (Shahaf et al. 2020), and PHOEBE (Prsa & Zwitter 2005).

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